Down-hole measurement of thermodynamic and geophysical parameters, increasingly deep and hot, of oil reserves is a cardinal factor for proper extraction. Measurement of these parameters is performed using tools that are designed specifically to endure the adverse environments of these applications. Some important parameters provided by these tools are temperature, pressure, flow rate, and vibrations, among others. The records of these parameters are useful for the characterization of reserves, since these tools are in direct contact with the formation thereof.
The depth of oil wells increases gradually and nowadays, in some cases, it exceeds 7000 m. Consequently, at those depths it is possible to obtain high-temperature and high-pressure conditions. Temperatures may exceed 200° C. and pressures may exceed 20,000 psi. It is considered high temperature above 150° C. and high pressure above 10 000 psi.
The measurement and recording of the characteristics of oil reserves has driven the design and implementation of measuring tools with specialized electronics and innovative communications systems. The challenges of communication systems, in these hostile environments, which lead to obtaining very poor signal-to-noise ratios (SNR), include noise interference, cable attenuation, and thermal drift of passive electronic components, among others.
The state of practice is integrated by technologies that use cable connections for communications and power transmission. Various communication techniques have been described, for example:
U.S. Pat. No. 4,107,644 describes a system and method to digitally transmit down-hole measurement information; signal transmission via cable is performed on baseband (without modulation) by means of a synchronization system with phase encoding. However, the intelligent communication system presented here does not have the electronic circuits or the method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses.
U.S. Pat. No. 4,355,310 describes a communications system for down-hole data capture that uses bidirectional communication with universal interconnection and addressing, which recognizes the control instruction from devices based on that addressing. However, unlike the intelligent communication system presented herein, this patent does not have the electronic circuits or the method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses.
U.S. Pat. No. 4,415,895 describes a data transmission system that uses bidirectional transmission-reception by means of modulation by PCM-pulse encoding. However, this patent does not consider the electronic circuits or the Method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses.
U.S. Pat. No. 5,838,727 describes a device and a method to transmit and receive digital data over a bandpass channel. It comprises a method and a device for transmission and reception combining amplitude modulation with QAM-phase modulation. However, this patent does not consider the electronic circuits or the method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses.
Patent US 2010/0052940 uses switched power line communication at frequencies greater than 400 kHz, and the transmission of communication signals is sent at low frequency, which causes switched power transmission not to interfere with communication. However, unlike the intelligent communication system presented herein, this patent does not have the electronic circuits or the method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio, and comparison with reference attenuation responses.
The aforementioned patents do not consider adaptive bidirectional transmission-reception equipment for communication using coaxial cable as linking medium, with a transmitter having operating-band automatic adjustment based on real-time frequency response of the communication link and the assessment of the signal-to-noise ratio for data transmission, the use of adjustable coupling and filtering devices for transmission and reception bands, a control module capable of measuring attenuation responses in transmission and reception to determine operating frequencies, and an intelligent receiver with operating-band automatic adjustment capability that best fits to modulation techniques in data transmission and reception.
In addition, the aforementioned patents do not deal with a method for real-time characterization of the attenuation response of a bidirectional communications system using coaxial cable as linking medium, by the generation of sweep signals by test tones or time-domain narrow pulse signals with known wide spectrum to characterize bands of interest covering transmission and reception bands, processing and measurement of received signals, comparison with reference responses, adjustment of transmission and reception frequencies to maintain communication with the maximum signal-to-noise ratio.